IOSR Journal of Applied Geology and Geophysics (IOSR-JAGG) e-ISSN: 2321–0990, p-ISSN: 2321–0982.Volume 4, Issue 1 Ver. I (Jan. - Feb. 2016), PP 58-68 www.iosrjournals.org DOI: 10.9790/0990-04115868 www.iosrjournals.org 58 | Page Petrophysical Evaluation of Middle Jurassic Reservoirs, Shams Oil Field, North Western Desert, Egypt. Eysa, E. A. Geology Department, Faculty of science, Zagazig University P.O. Box. 44519, Zagazig, Al Sharqia, Egypt. Abstract: The Western Desert is one of the most promising areas for hydrocarbon exploration and production in Egypt. The present work aims to evaluate the petrophysical reservoir characteristics and the lithology of Middle Jurassic Upper Safa reservoir (middle part of Khattatba Formation) in Shams oil field, North Western Desert, Egypt. Five wells (Shams-1x, Shams-2x, Shams-3, Shams-4 and Shams-8) were utilized for this study. They are analyzed for evaluating the different petrophysical parameters of the Middle Jurassic Upper Safa reservoir. The well log analysis of the Upper Safa reservoir, including data editing and data correction, are used in determination of lithology and porosity using density-neutron crossplots. The results of density-neutron cross plots revealed that, the lithology of Upper Safa reservoir is mainly sandstone with some calcareous cement. A weak effect of natural gas appears by shifting the plotted samples to the up-left of sand line. The porosity in the five wells ranges from 5% to 15% indicating fair porosity. Petrophysical parameters of the Upper Safa reservoir are illustrated in vertical litho-saturation crossplots to delineate the most effective sand zones in each well. Movable hydrocarbon increases mostly at the top and middle parts of the target reservoir in the studied wells. The iso-parametric maps of the Upper Safa reservoir show that, the northern and northwestern parts of Shams oil field are the most promising areas for future development. Keywords: Middle Jurassic, Petrophysical Evaluation, Shams oil Field, North Western Desert. I. Introduction The Western Desert is an important hydrocarbon producing region and has been intensely explored since the middle of the last century [1 & 2]. The study area is located in Shoushan Basin, Northern Western Desert, Egypt. It lies between latitudes 30° 48’ - 30° 51’ N and longitudes 26° 53’ – 26° 57’ E (Fig. 1). The northern part of the Western Desert consists of a number of sedimentary basins that received a thick succession of Mesozoic sediments. The sedimentary section in the northern part of the Western Desert can be divided into three sequences based on lithology, namely: the lower clastic unit from Cambrian to pre-Cenomanian, the middle carbonates from Cenomanian to Eocene and the upper clastic unit from Oligocene to Recent [3]. The Mesozoic sequence overlies unconformably Paleozoic rocks. The Mesozoic stratigraphic succession is much better understood than the Paleozoic one as it is encountered in all studied wells as indicated by [4, 5, 6, 7, 8, 9, 10& 11]. Figure (2) illustrates the simplified stratigraphic section in the Western Desert. The Middle Jurassic sandstones of the Khatatba Formation are an attractive petroleum exploration target in the northern part of the Western Desert. [12] indicated that, Khatatba Formation at the eastern margin of Shushan basin is mainly composed of sands interbeded with overbank organic-rich shales and coals, reflecting fluvio-deltiac deposits of fluviatile and tidally influenced channel. It is overlain conformably by Upper Jurassic Masajid Formation. Among the key references dealing with the petroleum systems in the north Western Desert are: [13, 14, 15, 16, 17, 18, 19 & 20]. The structural setting of the North Western Desert has been discussed by many authors such as, [21, 3, 22, 23, 24& 25] and others. The main objectives of this study are to determine the reservoir lithology and porosity using Density- Neutron crossplots, identify the different reservoir parameters characterizing the pay zones and construct iso- parametric maps from well log data to delineate the most effective sand zones and spot light on the promising locations for other further exploration. II. Materials And Methods The studied wells are: Shams-1X, Shams-2X, Shams-3, Shams-4 and Shams-8. The available well logs are density, neutron, gamma ray, resistivity, caliper, and sonic logs. The interpretation of lithology and porosity of the Upper Safa reservoir was undertaken using all the logs registered through a systematic approach, they were determined from logs using some chart types of neutron-density crossplots [26] . The neutron-density crossplots are commonly used to determine the lithology and accurately evaluate the porosity of the reservoir rocks. The effect of light hydrocarbons (natural gas) can be observed on the cross plot, where the plotted points tend to shift north-westerly from the sandstone line. Also, the effect of shale can be observed on the crossplot, where the shale effects tend to be in the lower-right quadrant of the crossplot [27].